1. Technical Field of the Invention
The present invention relates to rotors for electric rotary machines and, more particularly, to a rotor for an electric rotary machine having permanent magnets each disposed between adjacent claw-shaped magnet poles formed on a pair of field iron cores.
2. Description of the Related Art
In the related art, a technology, disclosed in, for instance, Patent Publication 1 (Japanese Patent Application Publication No. H08-223882), has heretofore been known as an alternator for an automotive vehicle or the like. With such a structure of the related art, a technology has been proposed contemplating the provision of a pair of Lundell type pole cores formed with claw-shaped magnet poles held in meshing engagement with each other with given clearances in which permanent magnets are inserted, respectively. This results in a reduction in leakage of fluxes between circumferentially adjacent claw-shaped magnet poles with a resultant increase in the amount of magnetic fluxes effective contributing to an effect of generating electric power, thereby achieving improved output.
With the related art structure mentioned above, further, each of the claw-shaped magnet poles has circumferentially spaced sidewalls whose outer peripheral portions are formed with flanged engaging stop portions extending in a circumferential direction. Each of the permanent magnets has outer peripheral shoulder portions held in abutting engagement with inner peripheries of the flanged engaging stop portions of the adjacent claw-shaped magnet poles. This restricts the permanent magnets from flying out of their assembled positions in a centrifugal direction (in a radially outward direction) during the rotation of the rotor.
Further, a support ring, made of non-magnetic material, has an outer circumferential surface to which a plurality of permanent magnets are fixedly secured by means of adhesive or the like to be structured as a magnet assembly, which in turn is assembled to the pole cores.
With the related art technology disclosed in Patent Publication 1, however, since the plurality of permanent magnets are fixedly secured to the support ring on the outer circumferential surface thereof by means of adhesive or the like, there is a need for component parts with extremely high precisions and increased assembling precision. That is, when placed in the magnet assembly, the plurality of permanent magnets are preliminarily fixedly secured in position with respect to the support ring. Under such a condition, if the permanent magnet is dislocated from a correct position in some degree, then, undue stress occurs on the permanent magnet when inserting the permanent magnet into the space between the circumferentially adjacent claw-shaped magnet poles or during use of the rotor, potentially resulting in damage to the permanent magnet.
Furthermore, even if the magnet assembly has high precision (i.e., increased positional precision of the permanent magnet with respect to the support ring), it is likely that a variation takes place in machining precisions of the claw-shaped magnetic poles. In this case, even if airspace (hereinafter referred to as a “magnet insertion space”) can be ensured enabling the permanent magnet to be inserted between the circumferentially adjacent claw-shaped magnet poles with the pair of pole cores being assembled, there is a likelihood that a deviation occurs between the magnet insertion space and the permanent magnet fixedly secured onto the support ring. This can cause a difficulty to arise in inserting the permanent magnet into the magnet insertion space.
With such a structure disclosed in Patent Publication 1 as set forth above, in order to allow a plurality of permanent magnets, fixedly secured onto the support ring, to be inserted to the magnet insertion spaces in multiple locations with no problem, not only the pole cores need to have increased part precisions (especially the claw-shaped magnetic poles need to have increased machining precisions) and assembling precision but also the magnet assembly needs to have increased precision. This results in a cause of an increase in production cost.